Re: for_each_online_cpu broken ?

Dave Jones
2005-12-08T05:33:09Z

On Thu, Dec 08, 2005 at 06:26:32AM +0100, Andi Kleen wrote:

Hi Andi,

> > Whilst debugging a memory leak, I hit sysrq meminfo,
> > and got hot/cold info for CONFIG_NR_CPUS rather than 4 cpus
> >
> > I've only tried reproducing this on x86-64 so far.
>
> If the online map is wrong all kinds of things would go wrong.
>
> Most likely your kernel doesn't have the fix.

This was seen with a .15rc5-git1 kernel.
Is this something still living in your x86-64 patchset or -mm ?

> The possible map is fixed kind of BTW in 2.6.15rc*. It was a side effect
> of CPU hotplug, which now uses a better algorithm to guess the
> number of possible CPUs. In 2.6.15 you will just get half the number
> of available CPUs in addition by default

Yep, I noticed it offers a maximum of 6 cpus on my way.
As a sidenote, seems kinda funny (and wasteful maybe?), doing this
on a lot of hardware that isn't hotplug capable. (Whilst I could
disable cpu hotplug in my local build, this isn't an answer for
a generic distro kernel).

Dave